The present invention relates generally to fluid control valves and, more particularly, to butterfly valves for controlling the flow of high temperature gases, such as, for example, hot gases downstream from an electric steel making furnace. The butterfly valve of the present invention is particularly suited for use in the main gas duct on the outlet side of a gas preheater for diversion of hot gas flow to a stack or to an air cleaner means or vice versa. The hot gas conduit or "main", as it is sometimes called, is relatively large in steel making operations, generally on the order of about 4 feet in diameter. In such applications, the usual service temperature facing the flow control valve is about 700.degree. to 800.degree. F., with excursions of upwards of 1000.degree.-1500.degree. F. or higher possible. It is observed that steel components may become plastic at such high temperatures. When such temperature excursions occur, harmful deformation and subsequent valve failure oftentimes result.
Some prior attempts have been made to provide a partially water-cooled butterfly valve wherein coolant water is introduced to the rotatable disc portion of the valve at one side thereof and withdrawn at an opposite side. Such valves have not proven to be totally satisfactory. Exemplary of prior fluid cooled butterfly valves are the devices disclosed in U.S. Pat. Nos. 2,517,596 and 2,811,981 to Parducci and Harris, respectively. The flow pattern of coolant water across the disc is non-uniform in these prior devices, resulting in low-flow rates or the formation of actual stagnant areas in the outer regions of the disc. Such flow irregularities cause localized hot spots to form on the disc surfaces. Deformation and poor sealing results, if not total disc failure when coolant flow irregularities occur. Further, prior butterfly valves have failed to provide adequate combined disc and body cooling which is needed to prevent deformation along the sealing surfaces of the valve disc and body.
The present invention solves many of the problems heretofore encountered in large diameter, high temperature applications by providing a butterfly valve in which the rotatable disc, the mounting shafts and the stationary body are all internally cooled by a fluid such as water. The valve disc is provided with a plurality of internal baffles to provide a tortuous yet uniform flow pathway for the cooling fluid and achieve uniform cooling across all surfaces of the disc. Localized water stagnation and hot spots on the disc surfaces are eliminated in the valve of the present invention. High coolant fluid flow rates prevent scale formation and attendant decreased heat exchange efficiency problems common in prior devices. The present invention further provides a butterfly valve which includes an improved gas seal means along the outer perimeter of the disc to achieve improved sealing efficiencies of upwards of 98% and higher. The invention further includes a hollow disc having a high strength construction which provides increased safety in the unlikely event cooling liquid should become trapped within the disc. The high strength disc is provided with reinforcement to contain internal steam pressure so generated. The butterfly valve of the present invention still further includes fluid cooled shafts to support the rotatable fluid cooled disc to provide correspondingly high flow rates of coolant fluid and a unique gas/fluid sealing arrangement in the shaft/hub assemblies.
The butterfly valve of the present invention further provides a valve body having a fluid cooling jacket adjacent an inner sidewall sealing surface to provide an improved gas seal. The body cooling jacket also provides a back-up cooling system in the event of blockage or failure in the disc cooling system so as to prolong the life and sealing capabilities of the valve assembly In addition, the cooling jacket construction of the valve body is of a double wall configuration which provides a body structure having greater strength than that of the main gas conduit. The increased structural strength and rigidity of the body provided by the double wall cooling jacket construction eliminates the need for auxiliary support posts or other support structures as commonly required in large conventional valve bodies.
Still further, the present invention provides a butterfly valve having improved coolant flow rates at the restricted hub areas of the valve body to ensure uniform fluid flow and cooling around the periphery of the body. The gas seal area of the valve body also provides a seat area constructed of a higher hardness metal which resists wear caused by abrasive particulate materials which may be carried in the gas stream. Since wear of the sealing seat is resisted, a uniform sealing interface is maintained along the periphery of the valve disc to ensure minimum gas leakage and correspondingly high sealing efficiencies. A sealing strip of high temperature braided Inconel material around the disc provides high abrasion resistance and offers superior resilience to ensure long term sealing efficiency.